An IGBT, which is a common power device, is popular one among high-current switches, and is widely used for a case with a high voltage and high current, such as the case with an operation voltage of 1200V.
IGBTs include flat IGBTs and trench IGBTs depending on the structures of their gates, and structural features and respective characters of the flat IGBTs and trench IGBTs are well known by the skilled person in the prior art. A manufacture process for any of the flat IGBTs and the trench IGBTs includes the front side processing and the back side processing, where the front side processing is used to form a gate (referred to as G for short) and an emitter (referred to as E for short) of the IGBT, and the back side processing is used to form a collector (referred to as C for short) of the IGBT.
Generally, the existing Trench IGBT is manufactured by either of two methods below.
The first method includes: conducting the front side processing on a monocrystal silicon substrate, thinning the back side of the substrate, and performing ion injection on the back side of the substrate for several times to form a collector. This first method is independent of an epitaxy process, but is dependent on high-energy ion injection and annealing activation processes, thus the high cost of a high-energy ion injection device causes a high cost for implementing the high-energy ion injection process; further, the activation rate of the doped source in the collector region formed by the ion injection and annealing is low, leading to poor saturation feature of the IGBT.
The second method includes: forming a relatively thick epitaxial layer on a monocrystal silicon substrate by reverse epitaxial growth, conducting the front side processing on the epitaxial layer, and then thinning the silicon substrate at its back side to form a collector. Here, the epitaxial technology is employed in this second method and an IGBT is mainly manufactured at this epitaxial layer (that is, all layers above a buffer layer are formed by the epitaxial layer), thus the epitaxial layer is relatively thick and is required to have a very good performance (such as the number of defects). However, it often happens that bad quality of the epitaxial layer leads to bad performance (for example, bad endurance for overvoltage and overcurrent) or low yield of the IGBT.
In view of this, it is necessary to provide a new manufacture method for a Trench IGBT in order to promote the performance of the Trench IGBT.